When an eccentric error is generated between magnetic heads in a magnetic disk device having plurality of magnetic heads mounted thereto, this eccentric error causes a positional error or a speed error upon seeking and changing a head. This might increase a seeking time, and deteriorate a seek performance.
A virtual-circle control might be executed in order to eliminate the eccentric error between the magnetic heads. In the virtual-circle control, the trajectory of the magnetic head is controlled so as to form a true circle around a rotation center of the magnetic disk.